DEVELOPMENT OF COMPTON CAMERA PROTOTYPE FOR HADRONTHERAPY MONITORING AND MEDICAL IMAGING

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DEVELOPMENT OF COMPTON CAMERA

PROTOTYPE FOR HADRONTHERAPY

MONITORING AND MEDICAL IMAGING

Jean-Luc Ley, J. P. Cachemiche, M. Dahoumane, Denis Dauvergne, Nicolas Freud, J. Krimmer, Jean Michel Létang, X. Lojacono, Voichita Maxim,

Gerard Montarou, et al.

To cite this version:

HADRONTHERAPY MONITORING

DESIGN OF THE CAMERA FOR HADRONTHERAPY MONITORING

PROTOTYPE DEVELOPMENT

REFERENCES

LEAKAGE CURRENT MEASUREMENT

MEDICAL IMAGING

STATE OF THE ART IN HADRONTHERAPY MONITORING

STATE OF THE ART IN MEDICAL IMAGING

DESIGN OF THE CAMERA FOR MEDICAL IMAGING (preliminary results)

ONGOING

ION BEAM THERAPY INTERESTS

The two main advantages for using ion beam in cancer treatment are:

• Ballistic precision (Bragg peak) (p and 12C)

• Relative Biological Effectiveness (RBE) of ions is better than the one of photons (>1) (12C)

ION-RANGE MONITORING Why?

• Ion range very sensitive to patient mispositioning, morphological changes...

• Risk: organ at risk could be over irradiated and/or tumor under irradiated

Goal?

• Online correction or cutting off of the treatment

How?

• Detection of the secondary particles emitted during nuclear fragmentations

RADIATION USED IN THE PRESENT WORK: PROMPT GAMMA

Correlation between prompt gamma proﬁ les and ion ranges.

CHALLENGES

• Compton scattering detection

• Discrimination between the background (mainly neutrons and protons) and the prompt gamma

• Time of ﬂ ight (hodoscope) > Very high counting rates

> Need high temporal resolution (~ ns)

• Large energy continuous spectrum of the prompt gamma (0.1 - 20 MeV)

• Random coincidences

APPLICABILITY OF PROMPT GAMMA DETECTION TO ION RANGE MONITORING

With a collimated camera and for homogeneous targets, the ion-range monitoring can be considered at a pencil-beam basis for proton beam and at an energy-slice basis for carbon ion beam. See Table 1. A Compton camera could improve dramatically the detection efﬁ ciency.

* Heidelberger Ionenstrahl-Therapiezentrum, Germany

PROTOTYPES BUILT IN THE WORLD

The idea to use a Compton camera for the medical imaging was launched by Singh in 1987. Since, different Compton cameras were developed, but none has reached a high enough level of performance to be commercialized.

Different technologies are developed to detect and characterize the Compton scattering.

• Single Compton scattering: Gunma university (Japan) [Takeda2012], university college London (United Kingdom) [Alnaaimi2011], Collaboration Compton Imaging for Medical Application (CIMA) [Llosa2006]

• Double Compton scattering: Hanyang university (Republic of Korea) [Seo2010] • Electron Tracking: Kyoto university (Japan) [Kabuki2010]

INTERESTS

In medical imaging, the initial photon energy is known (specific isotope). It is thus possible to select good or bad events with the total energy deposit in the camera.

The present Compton camera should:

• Have a better detection efﬁ ciency than the SPECT* in nuclear imaging (no physical collimator) • Have a direct 3D image reconstruction

• Use radiopharmaceuticals with a higher energy photon than what is used currently (PET** maximum: 511 keV) > Less attenuation in the patient

* Single photon emission computed tomography. ** Positron emission tomography.

• Different sorts of system have been developed to detect prompt gamma-ray like knife edge slit camera [Smeets2012], collimated camera with TOF [Testa2010] or without TOF [Min2012] and Compton camera [Richard2011].

• Examples of Compton camera prototypes which are in development:

> European project (ENVISON): university of Valencia [Llosa2012], university of Dresden [Golnik 2011], university of Lyon [Richard2011] > Korean project: university of Hanyang [Seo2011]

SIMULATED PHYSICS

• Monte-Carlo simulation: Geant4.9.4 • Electromagnetic processes

• Taking into account the Doppler broadening and the photon polarization

RESULTS

• ARM* distribution is fitted by the Voigt function: convolution of Gaussian and Lorentzian functions.

• The ﬁ gure of merit is the angular resolution of the camera (ARM*) • ARM improves with energy of photon

• The ARM is 3.8 ° at 1 MeV > Need for setup optimization

* Angular Resolution Measure: value of the full width at half maximum (FWHM) of the distribution of differences between the real and measured angles.

SIMULATION GEANT4

• In the ﬁ rst stage, modiﬁ cation of the "hadrontherapy" prototype for medical imaging purpose • The current parameters of this camera are gathered in Table 2

COMPTON CAMERA PRINCIPLES 1. Tumor irradiation

• Incident ions are tagged in position and time by a hodoscope

• Nuclear fragmentation occurs in the patient body • Prompts gamma-rays are emitted

2. Detection with the Compton camera

2 interactions:

• 1 interaction in a single layer of the scatterer stack (silicon)

• 1 interaction in the absorber detector (BGO)

> Total absorption of the photon in the camera is assumed

• The 60 cm distance between the patient and the absorber are mandatory to perform TOF measurement

3. Emission point reconstruction

1st_method

• The intersection between the ion trajectory (provided by the hodoscope) and the reconstructed cone of the Compton camera.

2nd method

• Iterative reconstruction with List Mode MLEM* [Lojacono2013]

* Maximum likelihood expectation Maximization

COMPTON CAMERA PROTOTYPE DESIGN

Compromise between the spatial resolution and the detection efﬁ ciency was found. The camera optimization has been carried out by means of Geant4 simulations (Fig. 4. [Richard2011])

THERE ARE THREE PARTS: THE HODOSCOPE, THE SCATTERER AND THE ABSORBER

1. Hodoscope

• Scintillating square ﬁ bers: 140 * 1 * 1 mm3

• Number of ﬁ bers: 2 * 128

• 8 PMs* Hamamatsu multianodes H8500 • Number of channels / PM: 64

2. Scatterer (DSSD** from Sintef)

• Number of layers: 7

• Dimensions: 90 * 90 * 2 mm3

• Number of strips: 2 * 64 • Pitch: 1.4 mm

3. Absorber (ﬂ uted BGO)

• Dimensions: 380 * 380 * 30 mm3

• Number of blocks: 100

• Dimensions per block: 38 * 38 * 30 mm3

• 4 PMs per block

All electronics (Front End and DAQ) for this hardware are in development.

* Photo-multiplier

** Double-sided Silicon Strip Detector

GOAL

• Characterization of the leakage current for each strip of each DSSD layer as a function of the temperature

• Leakage current is an important factor because it degrades the silicon energy resolution

MATERIALS

• Climate chamber: Weiss WTL 64 • Micro Ampere meter

• Speciﬁ c electronic card • 1 DSSD (2 * 64 strips) • High voltage: 750 V

METHODS

• Deplete all the silicon: 750 V on the 64 strips except the one which is measured

• Measure the strips for a range of temperature from +30°C to -40°C

RESULTS

• The leakage current drops down with the decreasing of temperature

• The minimum current leakage is 0.6 nA (- 40°C) • Good agreement between theoretical and

measured leakage currents [Speiler1998] > The DSSD will work at -20°C in a thermal

chamber (under development)

• Energy resolution’s estimation is 1.12 keV (FWHM) at - 20°C

INSTRUMENTATION

• Development of various electronic cards (Front End, DAQ, acquisition devices),

• Development of the thermal chamber for the DSSDs • Development of the acquisition program

• The ﬁ rst measurements with the prototype are expected for the beginning of 2014.

SIMULATION (MEDICAL IMAGING)

• Deepen the state of art

• Study of the parameters which could impact the camera’s spatial resolution and detection efﬁ ciency

• Optimization of a Compton camera for high energy gamma (more than 511 keV)

[Alnaaimi2011] Alnaaimi et al, Physics in Medicine and Biology 56, no 12 (21 juin 2011): 3473-3486. doi:10.1088/0031-9155/56/12/002.

[Dedes2012] Nuclear Science Symp., Medical Imaging Conf. & Workshop on Room-Temperature Semiconductor X-Ray and Gamma-Ray Detectors at press. [Fokas2009] E. Fokas et al, Biochimica et Biophysica Acta (BBA) - Reviews on Cancer, 1796(2):216 – 229, 2009.

[Golnik2012] In 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 3323-3326, 2011. doi:10.1109/NSSMIC.2011.6152600. [Kabuki2010] Kabuki et al, In Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE, 2844–2847, 2010.

[Llosa2006] Llosa et al, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 569, no 2 (décembre 2006): 277-280. doi:10.1016/j.nima.2006.08.028. [Llosa2013] Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 718 (août 2013): 130-133. doi:10.1016/j.nima.2012.08.074.

[Lojacono2013] X. Lojacono et al, Interdisciplinary Symposium on Signals and Systems for Medical Applications, Paris, France, 3-4 juin 2013. [Min2012] Min et al., Med. Phys. 39 (4), April 2012.

[Richard2011] Richard M.-H. et al, In IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 3496-3500, 2011. doi:10.1109/NSSMIC.2011.6152642.

[Seo2010] Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 615, no 3 (avril 2010): 333-339. doi:10.1016/j.nima.2010.02.060. [Seo2011] Seo et al, Journal of Instrumentation 6, no 01 (11 january 2011): C01024-C01024. doi:10.1088/1748-0221/6/01/C01024.

[Smeets2012] Smeets et al, Physics in Medicine and Biology 57, no 11 (7 juin 2012): 3371-3405. doi:10.1088/0031-9155/57/11/3371. [Spieler1998] H. Spieler, SLUO Lectures on Detector Techniques, October 30, 1998.

[Takeda2012] Takeda et al, Nuclear Science, IEEE Transactions on 59, no 1 (2012): 70–76. [Testa2010] M. Testa, Radiat Environ Biophys (2010) 49:337-343.

Fig. 2. Secondary particles’ rate

produced by nuclear frag-mentation for ion beam of

12_{C at 310 MeV/u in}

wa-ter (simulations Geant4). [Dedes2012]

Fig. 3. Conﬁ guration of the monitoring

system: the prompt gamma-ray emission points are recons-tructed by intersecting the ion trajectory and the Compton cone. The ion trajectory is obtained with the hodoscope and the Compton cone is reconstructed with the camera. Time of ﬂ ight (TOF) measurements between the absorber detector and the beam hodoscope (with an ap-propriate delay) are performed. [Richard2011]

Fig. 4. Reconstructed proﬁ le in the case

of a beam with the IBA time structure and of detectors with realistic energy, position and time resolution. 2.108_incident

protons at 160 MeV were shot. The position of the target is indicated by a light blue back-ground. The conclusion is the limited performances of the Compton camera because of the high rate of random coinci-dences: fall-off retrieval preci-sion of about 2.5 mm (standard deviation) with 2.108_protons

[Richard2011].

Fig. 1. Depth dose distribution

for photons and monoe-nergetic Bragg curves for carbon ions and protons [Fokas2009].

Fig. 5. a. The hodoscope

b. 2 PMs Hamamatsu H8500 connected via optic ﬁ bers (on each side) c. DSSD mounted on an electronic card

d. First prototype of an ASIC of the DSSD’s front end e. Block BGO (100 blocks compose the absorber) f. Each block is connected to 4 PMs

a b

c d

e f

Table 1. Orders of magnitude for applicability to ion-range

moni-toring with a collimated camera. The target was at 60 cm from the LYSO scintillator and the collimator in tungsten alloy had a slit of 4 mm. This experiment was made at clinical center of Heidelberg (HIT)*.

Table 2. Parameters used for the simulation of the Compton camera for medical imaging.

Number of particles 10 millions Number of layers of silicon 7

Distance source - ﬁ rst scatterer 100 mm Distance last scatterer - absorber 150 mm

Distance inter scatterers 60 mm Photon energy From 100 keV to 3 MeV

The absorber’s spatial resolution 5 mm The scatterer’s spatial resolution 1 mm

Equivalent Noise Charge 200 The absorber’s energy resolution 14%

Source Point source Emission angle Narrow angle

Beam Proton Carbon

No. of γ per ion ~ 1 - 2 x 10-7

No. of ions per energy slice ~ 10

10 _{~ 10}8

per spot ~ 108 _{~ 10}6

No. of γ per energy slice 2000 20

per spot 20 0.2

Fig. 7. Electronic card built in order to

test the leakage current of the DSSD. The top card on the left is used to measure the n-side and the bottom card on the right is used to measure the p-side. The (a) pins are used to input the high voltage and the

(b) pins are used to extract the

signal.

a

a b

b

Fig. 6. Variation of the Compton camera’s ARM versus the different

monoenergetic photon energies. The ﬁ t of the ARM distribution is calculated by the Voigt function. The right scale is an estimation of the spatial resolution. In order to estimate this resolution, it uses a point of interaction in the scatterer located in the middle of the stack (135 mm from the source).

PRELIMINAR

Y

Fig. 8. Curent leakage measured in

function of temperature. The blue points are measures of strip 43 and the green ones are measures of strip 35 (strips 35 and 43 are normal strips). The measures of strip 43 are represented by the blue curve and the red curve represents the theoretical values of the leakage current (as deﬁ ned by the formula on the graph). Ip(T) ∝T2×e